1. Field of the Invention
This invention relates to air pollution control. More specifically, the invention is directed to a reactor and method for insuring oxidation of oxidizable materials in waste gas streams, and particularly by means of a waste gas purifier such as a catalytic oxidation unit. More particularly, the invention relates to a reactor and method whereby a substantially uniform flow is maintained across the surface of one or more catalyst beds.
2. Description of the Prior Art
Considerable effort has gone into removing harmful materials present in waste gas streams such as would be present in industrial plants such as those waste gases produced in the production of maleic anhydride. In developing waste gas purification units for such waste gas streams, one problem that arises is the low percent oxidation of the oxidizable components of the waste gas streams. This is particularly true in catalyst systems where it is necessary to make the catalyst beds relatively thin, such as from about 1 to 8 inches in depth, in order to prevent catalyst attrition and due to the high cost of the catalyst. Also, in some of these catalyst beds, such as those composed of oxides of manganese and copper, in order to prevent overheating of the catalyst and to minimize the energy needed to preheat, the waste gas is preheated only to the temperature needed to oxidize one of the contaminants, e.g. carbon monoxide (CO). The heat released by oxidation of the CO heats the gas to the ignition temperature of the other contaminants--hydrocarbons. Thus, the portion of the catalyst bed able to completely oxidize the hydrocarbons is small, which means that only a very thin layer of the catalyst bed is useful for conversion of hydrocarbons. If there is a disproportionately higher flow of gas to one section of a catalyst bed, the CO conversion will tend to decrease and therefore provide less heating of the gas. The lower gas temperature in turn will diminish or perhaps prevent the oxidation of hydrocarbons.
Nagamatsu, U.S. Pat. No. 3,719,457, describes a catalytic converter for purification of motor vehicle exhaust gases. This reference does teach the use of a flow control baffle to "reduce exhaust gas turbulence and velocity inequities" between the flow control baffle and the catalyst bed. However, there is no indication of a problem of uniform distribution of the exhaust gases across a "thin" catalyst bed or one with a temperature gradient across it. Furthermore, this reference requires the flow control baffle have an open area of at least 25 percent. Furthermore, the reference indicates that the spacing between the catalyst bed and the flow control baffle is not critical--since apparently the only concern of this reference is cutting down on the gas stream turbulence.